Authorities in Iran have issued an arrest warrant for an acclaimed Iranian lawyer and arrested his wife and brother-in-law over his involvement in the case of a woman sentenced to death by stoning.

Lawyer Mohammad Mostafaei's office in Tehran was ransacked, and he was interrogated in Evin prison for four hours on Saturday over his human rights activities and involvement in the case of Sakineh Mohammadi Ashtiani, the 43-year-old mother of two who was convicted of adultery and whose plight in Iran has drawn international attention since her children launched a campaign for her release almost a month ago.

Mostafaei called Sakineh's stoning sentence "a bogus conviction" and "absolutely illegal" in an interview with the Guardian earlier this month.

He was released, then called back for further questioning before being set free. Authorities then issued an arrest warrant.

When they were unable to find him the authorities arrested his wife, Fereshteh Halimi and her brother Farhad Halimi to try to force him to surrender. However, it is still unclear whether Mostafaei has been arrested or he has managed to evade officials.

"It is ridiculous that they [officials] have taken Mostafaei's family as ransom, they have somehow taken them hostage. This confirms what Sakineh's son wrote in his public letter, that there's no justice in Iran," said Mina Ahadi, a human rights activist for Iran Committee against Stoning (ICAS), based in Germany who spoke to Mostafaei after he was interrogated.

"Mohammadi Ashtiani's sentence is not Mostafaei's first stoning case, he has defended many others against execution by stoning but it was Sakineh's story which took world attention and made the Iranian authorities angry," she said.

Mostafaei initially wrote an open letter about Sakineh's death by stoning after her sentence was handed down. He then tried to publicise her case by giving interviews to international media and helping her children launch the campaign for their mother's release.

Unlike his well-known Iranian colleagues Shirin Ebadi, a peace Nobel laureate and Shadi Sadr, a winner of Human Rights Defenders Tulip awards 2009 who were forced to leave Iran, Mostafaei was still working inside Iran although he was arrested for a while last year.

"Mostafaei is not a normal lawyer, he is also a human rights activist and he has represented several stoning cases and juvenile offenders in Iran," said Soheila Vahdati, an Iranian activist who is based in California.

"Mostafaei writes regularly for Iranian media and his blog and his role in making Iranians aware of the human rights abuses in Iran has made it difficult for the Iranian regime to tolerate him anymore," she said.